This invention relates generally to piezoelectric transducers, and more specifically provides an improved piezoelectric diaphragm which can be used as a sensor, or in fluid ejection applications.
Piezoelectric transducers have many applications. In particular, piezoelectric diaphragms have been employed as pressure sensors, in speakers for audio equipment, fluid ejection, fluid pumping and printing applications. The basic principles for the operation of piezoelectric transducers are as follows. A piezoelectric material having electrodes is bonded or deposited on one or both sides of a diaphragm material to form a piezoelectric actuated diaphragm. Diaphragms with piezoelectric material on one side only are referred to as uni-morph diaphragms, while diaphragms with piezoelectric material on both sides are referred to as bi-morph diaphragms. The piezoelectric actuated diaphragm can then be utilized in two modes.
The first mode is to apply a charge to the electrodes which creates a field across the piezoelectric material. The field will cause a strain in the piezoelectric material and the piezoelectric material and the diaphragm then moves. This first mode is very useful in applications such as fluid ejection applications or in audio equipment. In both cases, the piezoelectric diaphragm can be caused to oscillate in a useful manner. In the former case, to provide a force which will cause fluid to eject from a chamber and in the second case to cause a speaker diaphragm to oscillate and to reproduce sound.
The second mode of operation is the converse of the first. The piezoelectric diaphragm is subjected to a force, pressure, or displacement that will cause the diaphragm to bend or move. The physical movement of the diaphragm then causes polarization to take place in the piezoelectric material and a charge to be present on the electrodes. The diaphragm can thus be used as a sensor.
In many of these applications it can be desirable to use a piezoelectric material of a certain thickness. For instance, it may be advantageous to use sol-gel deposition to form the piezoelectric material resulting in a piezoelectric layer of approximately 1 micron thickness. Also, to achieve adequate sensitivity, as in sensor applications, or volume displacement, as in fluid ejection or audio applications, the area of the diaphragm must be of at least a minimum size. However, because a larger diaphragm will generally be less stiff, there are trade-offs between sensitivity or efficiency and stiffness in designing piezoelectric diaphragms. Therefore, there is a need to provide a thin film piezoelectric diaphragm that can provide both adequate sensitivity or efficiency while at the same time maintaining a desired stiffness.
There is provided a piezoelectric diaphragm system which can maintain both adequate stiffness characteristics as well as maintaining adequate sensitivity or displacement characteristics. This is achieved by utilizing an array of smaller diaphragms built onto a single chamber. As each individual diaphragm can be kept relatively smaller, then the size of each diaphragm can be designed to maintain the desired stiffness characteristics. However, using an array of diaphragms acting in parallel then allows the total area to be covered to be larger than any one sub-diaphragm to achieve the desired sensitivity or efficiency characteristics for the total chamber.
Further advantages will become apparent as the following description proceeds.